The frequency response or bandwidth of an electrical device is defined as that frequency where the output power amplitude is reduced by 3 dB, a factor of two, from its true value. For a p-i-n or avalanche photodiode the device frequency response is increased by narrowing the active region of the device, thus minimizing carrier transit time delays, and by reducing the cross-sectional area of the device, thus reducing the device capacitance. For avalanche and p-i-n photodiode light detectors the frequency response extends from dc to greater than several gigahertz, hereinafter GHz, but is typically limited by stray reactances in the light detector housing and by impedance mismatch to the external electrical circuitry.
Webb et al, U.S. Pat. No. 4,233,619 issued Nov. 11, 1980 and entitled LIGHT DETECTOR HOUSING FOR FIBER OPTIC APPLICATIONS and incorporated herein by reference, have disclosed an electro-optic device housing in which an avalanche or p-i-n photodiode can be mounted. The housing comprises a header; electrical signal and bias electrodes inserted through the header; a light detector mounted on one of the electrodes; means for electrically connecting the light detector to the electrodes; a cap, bonded to the header, which encloses the light detector; and a light pipe extending through an opening in the cap towards the light detector. Alternatively, the light pipe of Webb et al can be replaced by a window mounted on the cap. The upper limit to the frequency response of this device is about one GHz and is limited by stray reactances in the housing, and by impedance mismatch to the signal transmission line. It would be desirable to have a housing with reduced stray reactances and which can be matched directly to the signal transmission line in order to make use of the higher frequency response of the light detector.
Low et al, U.S. Pat. No. 3,705,255 issued Dec. 5, 1972, have disclosed a package suitable for housing microwave semiconductor components. The package comprises an electrically conductive stud having one end that is cylindrically shaped and another end that is conically shaped, wherein the conical end is flat so that a semiconductor component can be mounted thereon; a cylindrical flange extending outward from a point between the cylindrical and conical ends of the stud; an insulating ring mounted on the flange about the conical end of the stud; an electrically conductive washer mounted on the other side of the insulating ring; an insulating washer mounted on the other side of the electrically conductive washer and an electrically conducting cap mounted on the other side of the insulating washer. The stud, the electrically conductive washer and the cap form the external terminals of the housing and are connected to the different terminals of the semiconductor component mounted therein. This housing has reduced inductive and capacitive reactances, thus making it suitable for use with semiconductor devices such as transistors which operate in the GHz range. This device does not provide a direct match to an external transmission line or detector to obtain maximum frequency response.